Many portable devices, for example mobile telephones, are equipped with a display such as a glass or plastic display window for providing information to the user. Furthermore such display windows are now commonly used as touch sensitive inputs. In some cases the apparatus can provide a visual feedback and audible feedback when recording a touch input. In some further devices the audible feedback is augmented with a vibrating motor used to provide a haptic feedback so the user knows that the device has accepted the input.
Furthermore such devices typically also use electro-acoustic transducers to produce audio for earpiece and integrated hands free (IHF) operations as well as for alert tones. The moving coil dynamic speaker configuration used is typically relatively large in relation to the volume within the device and require specific signal processing considerations in order that the acoustic frequency response is acceptable. Furthermore moving coil transducers can attract contaminants such as small iron particles from within the internal volume of the device and also through ports provided to enable acoustic wave transmission from the speaker to the external environment. These contaminants can cause distortion and faults within the speakers significantly reducing the lifetime of the device.